In a device such as, for example, a flash memory, information is stored as electrons or holes are stored in a floating gate through a tunnel insulating film at the time of writing or erasing. With an increase in capacity and density of the flash memory, a nitride film having a high dielectric constant, for example, a SiN film is used for the tunnel insulating film. A SiN film with reduced structural defects is formed by, for example, atomic layer deposition (ALD).
In the ALD method, a substrate is exposed to a precursor gas containing constituent elements of a thin film to be formed on the substrate so that the precursor gas is adsorbed onto the surface of the substrate. Subsequently, the substrate is exposed to a purge gas to remove the precursor gas excessively adsorbed onto the surface of the substrate. Then, high frequency waves are supplied to a reaction gas containing the constituent elements of the thin film to be formed, thereby generating plasma of the reaction gas, and the substrate is exposed to the generated plasma, thereby forming the desired thin film on the substrate. In the ALD method, a film containing atoms or molecules contained in the precursor gas is formed on the substrate by repeating such steps. See, for example, Japanese Patent Laid-Open Publication No. 2014-135475.